This invention relates generally to a ballast for a fluorescent lamp, and more particularly to a dimmable, single stage fluorescent lamp.
A conventional single stage fluorescent lamp, such as disclosed in PCT Patent Application No. WO 96/07297, includes a ballast having an output (i.e. inverter) stage. No additional stage, such as a switch mode power supply, is required in maintaining a sufficient D.C. voltage across a buffer capacitor. Instead, the lamp ballast includes a feedback path for drawing sufficient current from the ballast input to maintain an appropriate charge across the buffer capacitor.
Many lamp ballasts are not designed for dimming. Unacceptably high overboost voltages can occur across the buffer capacitor during low level triac dimming (e.g. at about 10% of full light output) due to too much power fed back to the buffer capacitor through the feedback path.
Accordingly, it is desirable to provide an improved dimmable fluorescent lamp in which the amount of power fed back to the buffer capacitor during low level dimming is reduced. The improved dimmable fluorescent lamp, in particular, should substantially reduce overboost voltages across the buffer capacitor during low level dimming.